It doesn't look exactly like a no-op to me, but its close enough :) 
#!/usr/bin/perl --

use strict;
use warnings;
use Benchmark 'cmpthese';

Main( @ARGV );
exit( 0 );

sub Main {
#~     my $big = 'a' x 99999999; # out of memory for me :)
    my $big = 'a' x 9999999;
    cmpthese( -3, {
        'U' => sub { Fundef($big,'bar');  return; },
        'R' => sub { Ffednu($big,'bar');  return; },
        'V' => sub { Fvaria($big,'bar');  return; },
    });
}
sub Fundef { my (undef, $x) = @_; my $blah = 0; if($x){ if($_[0]){ $bl
+ah=1; } } return; }
sub Ffednu { my ( $x ) = $_[1]; my $blah = 0; if($x){ if($_[0]){ $blah
+=1; } } return; }
sub Fvaria { my ($var, $x ) = $_[1]; my $blah = 0; if($x){ if($_[0]){ 
+$blah=1; } } return; }

__END__

[download]
$ perl5.6.1.exe bench.895401.pl
Benchmark: running R, U, V, each for at least 3 CPU seconds...
         R:  2 wallclock secs ( 3.09 usr +  0.00 sys =  3.09 CPU) @ 97
+7555.91/s (n=3024558)
         U:  4 wallclock secs ( 3.08 usr +  0.00 sys =  3.08 CPU) @ 95
+7410.66/s (n=2946910)
         V:  4 wallclock secs ( 3.20 usr +  0.00 sys =  3.20 CPU) @ 10
+76184.20/s (n=3447018)
       Rate    U    R    V
U  957411/s   --  -2% -11%
R  977556/s   2%   --  -9%
V 1076184/s  12%  10%   --


$ perl5.6.1.exe bench.895401.pl
Benchmark: running R, U, V, each for at least 3 CPU seconds...
         R:  4 wallclock secs ( 3.27 usr +  0.00 sys =  3.27 CPU) @ 97
+9082.06/s (n=3197682)
         U:  3 wallclock secs ( 3.02 usr +  0.00 sys =  3.02 CPU) @ 98
+8797.75/s (n=2982214)
         V:  4 wallclock secs ( 3.08 usr +  0.00 sys =  3.08 CPU) @ 10
+55320.66/s (n=3248277)
       Rate   R   U   V
R  979082/s  -- -1% -7%
U  988798/s  1%  -- -6%
V 1055321/s  8%  7%  --


$ perl5.6.1.exe bench.895401.pl
Benchmark: running R, U, V, each for at least 3 CPU seconds...
         R:  2 wallclock secs ( 3.19 usr +  0.00 sys =  3.19 CPU) @ 99
+5011.92/s (n=3172098)
         U:  2 wallclock secs ( 3.09 usr +  0.00 sys =  3.09 CPU) @ 95
+2459.60/s (n=2946910)
         V:  2 wallclock secs ( 3.02 usr +  0.00 sys =  3.02 CPU) @ 11
+42910.48/s (n=3447018)
       Rate    U    R    V
U  952460/s   --  -4% -17%
R  995012/s   4%   -- -13%
V 1142910/s  20%  15%   --


########################################################
########################################################

$ perl5.12.2.exe bench.895401.pl
      Rate    U    R    V
U 773636/s   -- -12% -18%
R 883140/s  14%   --  -6%
V 941514/s  22%   7%   --

$ perl5.12.2.exe bench.895401.pl
      Rate    U    R    V
U 791225/s   --  -7% -16%
R 846669/s   7%   -- -10%
V 939247/s  19%  11%   --

$ perl5.12.2.exe bench.895401.pl
      Rate    U    R    V
U 785108/s   --  -7% -17%
R 843697/s   7%   -- -11%
V 944078/s  20%  12%   --

[download]

In reply to Re: Is undef list assignment a no-op? by Anonymous Monk
in thread Is undef list assignment a no-op? by repellent

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